Well I was wondering if with the teams running only the one driver per day, do they have a complete separate car for each driver or do they both use the car just with the numbers/lettering changed on the bodywork?

Very interesting, I would expect them to be testing different configurations on each car to see which one is better.

I wonder how they setup the car for Jerez – do they use a setup that would be close to the set up for the majority of tracks or a setup to suit Jerez? If it’s the former would that be a setup for the Tilkedromes?

Because of the amount of time it takes to actually get one car built, they generally get one done for the tests while finishing off the other one (plus spares). Means that they dont rush things and get 2 out that might be less reliable than getting one right in the timeframe. Plus a fair bit of it (apart from the tub) will be altered before the first race anyway so they may as well save the costs of making the extra parts and shipping them out there purely for testing.

A team has finite resources, everything has an opportunity cost.
If the team were to run two cars, they would have to build two of everything, which means they won’t be able to produce as many variations of parts.

Considering that most parts at this stage are prototypes, building two of something that might not work is a waste of resources (time, money and staff).

The benefit of running two cars at a test is negated by variables such as setup and driver, so any analysis between the cars would have to factor in that, making it less accurate.

@Michael Since they aren’t competing for the best lap time at testing, the car’s setup is handled differently. They aren’t looking for the fastest way of getting around Jerez, they are looking at a whole bunch of measurements with a variety of setups. Not having to find the optimum setup for that track allows them to run setups for anything from Monaco to Monza. They’re discovering how the car behaves with setup changes, which helps them dial a car into the track at races.